The surface membrane related characteristics which distinguish tumorigenic and nontumorigenic cells, derived from mouse mammary carcinomas and normal mouse mammary glands are being determined. The tumorigenic cells exhibit alterations in several classes of fucosylated compounds, namely fucosylated amino acids, trypsin-sensitive, surface fucopeptides and cell surface associated fucoproteins. As an approach to understanding the metabolism of the fucopeptides the mannose and glucose analog, 2-deoxy-D-glucose has been used. There is a differential effect on the trypsin-sensitive, surface fucopeptides when normal and transformed cells are cultured in medium supplemented with 2-deoxy-D-glucose. In addition there are small but consistent differences in the choline phosphatides of the tumorigenic and nontumorigenic mammary cells.